Grease 4-6 2-cup ramekins, or a 2 quart casserole dish. Set aside. Preheat oven to 350 degrees.
In a large mixing bowl, stir together the flour, 2/3 cup granulated sugar, 2 Tbsp. cocoa powder, baking powder, and 1/4 tsp. salt. Set aside.
In a small mixing bowl stir together the milk, nuts, melted butter, and 1 tsp. vanilla. Add to the dry ingredients and stir to combine. Pour into ramekins or casserole dish.
In another bowl, stir together the brown sugar, 1/4 cup granulated sugar, 3 Tbsp. cocoa powder, 1 tsp. vanilla, and 1/8 tsp. salt. Sprinkle the mixture evenly over the batter. Pour the boiling water evenly over each ramekin, or casserole dish.
Bake 30 minutes. Top with vanilla ice cream and serve immediately.